1. Field of the Invention
The present invention relates to an aluminum support for a lithographic printing plate (also called “a support for a lithographic printing plate” in the present invention), a method of preparing the same and a presensitized plate using the same. More particularly, the present invention relates to a method of preparing an aluminum support for a lithographic printing plate where a low-purity aluminum rolled plate (an aluminum plate containing much of alloy components or an aluminum plate with alloy components unadjusted) can be used in addition to an aluminum plate used for a conventional support for a lithographic printing plate, an processing unevenness is not generated by graining treatment and the plate can have an optimum surface shape achieving both high press life and printing performance (scum resistance performance) when a lithographic printing plate is prepared (from the aluminum support for a lithographic printing plate), the support for a lithographic printing plate obtained by the method thereof and a presensitized plate using the printing plate.
Further particularly, the present invention relates to a presensitized plate excellent in laser exposure suitability and printing performance (water receptivity, water wettability of a non-image area, press life, and scum resistance of a printing plate), a support for a lithographic printing plate which is a base material of the presensitized plate and a method of preparing the support for a lithographic printing plate.
2. Description of the Related Art
Graining treatment is generally performed on an aluminum support for a lithographic printing plate in one combination or more among mechanical graining treatment, chemical etching in aqueous acid or alkali solution, desmutting treatment in an aqueous acid solution, electrochemical graining treatment in an aqueous acid solution (electrolytic graining treatment), anodizing treatment in an aqueous acid solution, treatment for water wettability, sealing treatment or the like.
Particularly, since electrochemical graining treatment can easily obtain even profile irregularities, it has been generally used as a method of graining on an aluminum support for a lithographic printing plate. Particularly, it is general to use electrochemical graining treatment mainly in aqueous hydrochloric acid or nitric acid solution.
In electrolytic graining treatment mainly using aqueous nitric acid or hydrochloric acid solution that has been conventionally employed as it is said that even profile irregularities can be obtained, it is necessary to strictly control the alloy components of an aluminum alloy plate. In addition, since a grained shape largely changes if the composition of alloy components fluctuates, if the conditions of graining treatment are kept constant, there lies a problem that even profile irregularities can not be formed on an aluminum alloy plate composed of various aluminum materials, particularly an aluminum alloy plate containing much content of impure elements.
In addition, there lies a problem that a grained shape of even profile irregularities can not be formed, if a graining treatment under a condition in a certain range which is conventionally deemed to be optimum is performed on the aluminum alloy plate composed of various aluminum materials.
On the other hand, in recent years, it has been desirable that an aluminum rolled plate where the rolling process of an aluminum plate is simplified, a general-purpose aluminum plate, a cheap-priced aluminum plate are rolled by using an unadjusted ground metal where alloy components recycled from beverage cans or the like are used as an aluminum support for a lithographic printing plate from the viewpoints of energy saving and effective utilization of natural resources.
On the contrary, if an aluminum support for a lithographic printing plate is prepared by using an aluminum plate where the rolling process of an aluminum plate is simplified, an aluminum plate containing much of alloy components and an aluminum plate with alloy components unadjusted, processing unevenness called streak attributable to an aluminum crystal orientation is likely to be generated. In addition, in electrochemical graining treatment, there lies a problem that an even graining treatment can not be performed and a defect in external appearance (processing unevenness) takes place or printing performance (particularly, scum resistance performance) is poor.
Furthermore, although an aluminum support for a lithographic printing plate having the performance achieving both impression number (press life) and scum resistance is preferred as an aluminum support for a lithographic printing plate having an image forming layer formed by a photosensitive image forming material by infrared ray laser for a direct plate making, nevertheless, electrochemical graining treatment can not be evenly performed and it is difficult to prepare an aluminum support for a lithographic printing plate having the compatible performance achieving both press life and scum resistance if the alloy components of an aluminum alloy plate are not controlled.
In the meantime, a presensitized plate is prepared by forming an image recording layer (also called “image forming layer” in the present invention) such as photosensitive layers on the grained surface of a support for a lithographic printing plate prepared in the aforementioned step.
In recent years, a direct plate making system where exposure is performed by directly drawing a print image on a presensitized plate with a laser beam in accordance with a digital signal from a computer has become widespread fast. In addition, a direct drawing type presensitized plate which directly exposes an print image on a presensitized plate mounted on the offset cylinder of an offset printing press with a laser beam has been used.
Taken up as laser exposure type presensitized plates exposed with a laser beam for example are the presensitized plate where an aluminum support web with an anodized layer formed at density of 5 to 12 g/m2 is a base material as described in JP 61-48418 B, the presensitized plate where a sol containing a silver halide and a kernel reducing the silver halide into metal silver is applied on an aluminum support web as described in JP 63-260491 A, the presensitized plate where silicate treatment is performed on the surface of an aluminum support web on which an anodized layer is formed to form aluminum silicate at density of 2 to 8 mg/mm2 as described in U.S. Pat. No. 4,555,475 and the presensitized plate where silicate treatment is performed on the surface of an aluminum support web on which an anodized layer is formed, over which carbon black is further applied as described in EP 164,128 and the like.